1. Technical Field
The present invention relates to switching exchanges, and in particular to a method for transferring information between channels carrying synchronous information traffic and channels carrying asynchronous data packet traffic, and to switching exchange apparatus for interconnecting communication lines carrying synchronous information traffic and communication lines carrying asynchronous data packets.
2. Background Art
In communications, there is an increasing interest for the transmission of various kinds of information such as computer data and voice signals over the same network. This requires facilities for integrated services. Among these, switches or exchanges are important which can transfer streams of information or data bursts between various lines or channels which are connected to such exchanges or network nodes. Various prior systems have been designed to handle different kinds of traffic in an integrated manner.
For example, in a publication by G. J. Coviello entitled "Integration of Circuit/Packet Switching by a SENET Concept", Proceedings of the National Telecommunications Conference NTC 1975, pp. 42-12 . . . 42-17, a switching node is disclosed in which traffic of incoming lines is separated into two classes: Circuit-switched traffic and packet-switched traffic. One bus is provided for each class to allow separate switching; one bus transfers voice traffic into class I output queues, and the other bus transfers data packets by a packet processor into class II output queues. The Coviello publication provides no solution for the arbitration between input trunks for access to the bus for circuit-switched traffic.
European patent application No. 0,054,077 entitled "Method of Transmitting Information Between Stations Attached to a Unidirectional Transmission Ring", published in June 1982, describes a token ring communication system in which, besides irregular packets, also synchronous information can be transmitted by issuing a priority token in quasi-synchronous intervals. However, it has a problem in that the beginning of synchronous information transfer has to wait for the termination of any packet transmission in progress. The system is designed for locally interconnecting stations, and not as a switching node for interconnecting lines or trunks.
An article by T. Takeuchi et al., "An Experimental Synchronous Composite Packet Switching System", published in the Proceedings of the IEEE 1986 International Zurich Seminar on Digital Communications, pp. 149-153, describes a system for common handling of circuit-switched and packet-switched traffic. Multiple switch modules are interconnected by a high-speed ring. CS data from several channels are collected in composite packets which are sent from one module to another with an address. However, actual switching is done in these modules by slot interchange procedures usually found in TDM switching systems. Actual transfer of information over the ring is done in equal-length packets so that the composite CS packets as well as non-composite data packets must be partitioned into equal-length sections with additional sequence numbering. When circuit-switched calls are terminated, a rearrangement of all slots in the composite packets is necessary.